Chage tree icons base on node underlying data type

Hello,

I'm using a com.sencha.gxt.widget.core.client.tree.Tree. I would like to change the icon of a node based on the tree node's underlying data (and NOT on the fact that the node is leaf or not, this is not important).

What's the best way to achive this? I am using gxt 3.0.0 beta2 and gwtp